Antisense expression of the fasciclin-like arabinogalactan protein FLA6 gene in Populus inhibits expression of its homologous genes and alters stem biomechanics and cell wall composition in transgenic trees.

Yang Yang,Lei Yang,Haihai Wang,Cuiting Wang,Hongxia Zhang,Xiaoyan Gao,Chunmei Jiang

doi:10.1093/jxb/eru479

Abstract

Fasciclin-like arabinogalactan proteins (FLAs) play important roles in the growth and development of roots, stems, and seeds in Arabidopsis. However, their biological functions in woody plants are largely unknown. In this work, we investigated the possible function of PtFLA6 in poplar. Quantitative real-time PCR, PtFLA6-yellow fluorescent protein (YFP) fusion protein subcellular localization, Western blotting, and immunohistochemical analyses demonstrated that the PtFLA6 gene was expressed specifically in the xylem of mature stem, and PtFLA6 protein was distributed ubiquitous in plant cells and accumulated predominantly in stem xylem fibres. Antisense expression of PtFLA6 in the aspen hybrid clone Poplar davidiana×Poplar bolleana reduced the transcripts of PtFLA6 and its homologous genes. Transgenic plants that showed a significant reduction in the transcripts of PtFLAs accumulated fewer PtFLA6 and arabinogalactan proteins than did the non-transgenic plants, leading to reduced stem flexural strength and stiffness. Further studies revealed that the altered stem biomechanics of transgenic plants could be attributed to the decreased cellulose and lignin composition in the xylem. In addition expression of some xylem-specific genes involved in cell wall biosynthesis was downregulated in these transgenic plants. All these results suggest that engineering the expression of PtFLA6 and its homologues could modulate stem mechanical properties by affecting cell wall composition in trees.

Highlights

As a typical class of glycoprotein, arabinogalactan proteins (AGPs) are involved in various aspects of plant growth and development, such as pollen-tube growth (Levitin et al, 2008; Coimbra et al, 2009), apical cell expansion (Lee et al, 2005), stem development (Park et al, 2003), cell division and expansion (Yang et al, 2007), xylem differentiation (Motose et al, 2004), and root development (van Hengel and Roberts, 2003)
Quantitative real-time PCR, PtFLA6–yellow fluorescent protein (YFP) fusion protein subcellular localization, Western blotting, and immunohistochemical analyses demonstrated that the PtFLA6 gene was expressed in the xylem of mature stem, and PtFLA6 protein was distributed ubiquitous in plant cells and accumulated predominantly in stem xylem fibres
Western blot analysis showed that a large amount of PtFLA6 protein accumulated in the xylem but only a trace amount of PtFLA6 protein was detected in the phloem tissues of mature stems (Fig. 1B)

Summary

Introduction

As a typical class of glycoprotein, arabinogalactan proteins (AGPs) are involved in various aspects of plant growth and development, such as pollen-tube growth (Levitin et al, 2008; Coimbra et al, 2009), apical cell expansion (Lee et al, 2005), stem development (Park et al, 2003), cell division and expansion (Yang et al, 2007), xylem differentiation (Motose et al, 2004), and root development (van Hengel and Roberts, 2003). GhFLA1 plays an important role in fibre initiation and elongation by affecting AGP composition and the integrity of the primary cell wall matrix (Huang et al, 2013). Some FLA proteins are associated with wood formation and are expressed preferentially in differentiating xylem, their precise functions are yet to be further elucidated (No and Loopstra, 2000; Whetten et al, 2001; Lorenz and Dean, 2002; Qiu et al, 2008; Dharmawardhana et al, 2010)

Methods

Results

Conclusion